WASHINGTON — With tax rates set to rise next year and tax law more complex than ever, the presidential campaign should provide the perfect forum for a debate over tax reform.

But that isn’t what voters are getting.

Instead, President Barack Obama and Mitt Romney have clashed over bits and pieces of the tax code, while making sweeping charges about each other’s plans.

The latest example came during Wednesday’s debate at the University of Denver, when Obama sought to portray Romney’s plan as a “$5 trillion tax cut” that would require middle-income families to pay more. Romney’s retort: Obama’s proposed tax hikes would crush small businesses.

Not only do Obama and Romney disagree on many elements of tax policy, but they also aren’t driving toward the same goal.

Romney wants to simplify the tax code, arguing that business will invest more if they know the future of taxes and aren’t tied in knots by accountants. Obama sees value in preserving tax preferences that support lower- and middle-income workers and favored sectors such as domestic manufacturing.

While Romney’s goals are more ambitious, he has provided less detail about how he’d achieve them. Obama’s legislative plans are more modest, but he has spelled out what he wants to do and how he’d do it.

“Obama is not very ambitious, but we know in pretty great detail what he would do,” said Howard Gleckman, a resident fellow at the Urban Institute who edits its affiliated TaxVox blog. “Romney is talking about doing very ambitious tax reform but is only telling us about half of the transaction.”

Obama’s proposals

Obama’s proposals have been detailed in his budgets and his 2011 deficit-reduction plan, in which he calls for raising the top tax rate on individuals earning more than $200,000 — and married couples making more than $250,000 — from 35 percent to 39.6 percent. Obama also proposes limiting the value of tax deductions claimed by the wealthy.

Obama’s budget proposals don’t try to simplify the tax code. Instead, they have sought to expand tax breaks for low-income people and green energy, while curbing and cutting ones for oil and gas producers.

“Obama has shown very little interest through the course of his administration in real tax reform,” Gleckman said. “He is a guy who believes in using the tax code to provide incentives to people, whether it’s the Earned Income Tax Credit or the child credit or the green energy subsidies.”

At Wednesday’s debate, Romney attacked Obama for using the tax code to jump-start favored industries. “In one year, you provided $90 billion in breaks to the green energy world,” Romney said.

Romney’s tax-reform plan seeks to lower rates and broaden the base on which taxes are levied — by curbing or eliminating many of the tax deductions, credits and exemptions that reduce tax liability.

His big-picture goals: Cut current income tax rates by 20 percent, kill the estate tax and the tax on investment income for most taxpayers, reduce the corporate tax rate and eliminate the alternative-minimum tax.

Cutting so many taxes at once would cause federal revenue to plummet, increasing the budget deficit. The respected Tax Policy Center estimated Romney’s tax cuts, without offsets, would reduce federal revenue by $456 billion in 2015.

Romney insists his plan won’t raise the deficit because he’ll curb deductions, credits and loopholes for upper-income households. But until this week, he offered no specifics on how he would pare back those tax breaks.

Romney’s goals

At Wednesday’s debate, Romney said deductions could be capped at “$25,000, $50,000.” Or “one could follow Bowles-Simpson as a model and take deduction by deduction and make differences that way,” he said, citing the deficit-reduction plan written by former Sen. Alan Simpson and former White House chief of staff Erskine Bowles.

Obama has pounced on Romney’s lack of detail, labeling his GOP rival’s plan as a “$5 trillion tax cut,” as he did repeatedly during Wednesday’s debate. (The $5 trillion is a rounded-up, 10-year multiple of the Tax Policy Center’s $456 billion estimate.)

The claim that Romney is cutting taxes by $5 trillion only holds water if one ignores Romney’s promise to reduce deductions and loopholes.

Independent analysts still don’t have enough detail to estimate how the Romney plan would affect specific groups of taxpayers or its impact on federal revenue.

“You sit here and scratch your head and say by going from being not forthcoming at all to throwing out all these ideas, he has not done anything to illuminate how [the plan] would pay for itself,” Gleckman said.

J.D. Foster, an economist at the conservative Heritage Foundation, said Romney has described three principles of tax reform, which include reducing rates, while not increasing the deficit and maintaining the current progressivity of the tax code. Beyond that, the details are the domain of Congress, he said.

“The way you advance a policy of this sort is you say these are the principles,” Foster said. “Then you ask yourself, ‘Is it credible? Can you have a tax reform that meets all three criteria?’ And clearly you can.”

But providing too many details is considered unwise by campaign operatives. Invariably, tax reform is a tradeoff between reducing rates and giving up tax breaks. The equation won’t balance out for everyone.

“Nobody puts out a complete tax reform plan unless they want to go down to defeat,” Foster said.